Locked wound core



LOCKED WOUND CORE Filed OO'b. 19, 1959 7 6 Flg 4 2 Sheets-Sheet 2 /NVEA/TOR J. FLL/ FE7' erro/QMS Y United States Patent() LOCKED WOUND CORE Catharines, Ontario, Canada Filed Oct. 19, 1959, Ser. No. 848,889

8 Claims. (Cl. 336-213) `This invention relates to electric induction apparatus, and more particularly to improvements in wound magnetic cores for such apparatus.

One of the problems encountered in the construction of laminated cores for electric induction apparatus is that of magnetic saturation and core losses which occur because of the presence of joints in the laminated material which constitutes the magnetic core.

`It is conventional to form such cores of a plurality of strips of the desired magnetic material by bending or Wrapping successively layers or laminations of the strips about an arbor shaped to give the required core contiguration. These cores are generally in the shape of a closed loop having a hollow centre, and the ends of lthe strips forming the laminations are butt-jointed in order to form the closed loop. Unless a perfect butt-joint is achieved between the ends of each successive strip, the flux density in a joint'section of the core will be higher than in other sections, since the joints serve to decrease the cross-sectional area of the core wherever they occur. This i11- creased flux density is-undesirable since it causes increased core losses and other undesirable effects.

In addition, considerable difficulty has been experienced in the past in obtaining close engagement of successive laminations in such a core, and of assembling the core about the winding leg of the coil. Various methods of achieving these results have been suggested but, thus far, all have suffered from one or more disadvantages such as the requirement of strips of different sizes or of specialized techniques and equipment for winding.

' It is an object of this invention, therefore, to provide an improved form of wound strip core wherein a good ux path isprovided between'successive laminations.

It isa further object of this invention to provide such a wound strip core capable of being easily assembled about the winding leg of the core.

It is yet another object of this invention to provide such a wound strip core capable of being adapted to any desired shape or size required.

The invention broadly embraces a laminated metallic core comprising a plurality of strips of magnetic material wound successively one upon another. There are arplurality of joints between adjoining strips with suc ceeding joints being spaced apart circumferentially of the core. form length which results in the desired circumferential spacing and also aiords interchangeability of the strips. At each of the joints the inner end of the successive strip directly overlaps the outer end of its preceding strip a Preferably the strips are of substantially unidistance suleient to provide a good flux path there- "ice between. The overlapping ends of the adjoining ends are provided at each of the joints with their own separate interlocking means. Each of the interlocking means comprises a pair of separably interlocked elements attached to adjoining ones of the overlapping ends of the strips to positively retain such overlapping ends in tight face-to-face contact substantially over the entire overlapped area and to positively prevent separation of the overlapped ends vradially of the core.

The strips of magnetic material are pre-cut, preferably in identical lengths. These strips are wound flatwise around a circular arbor with the overlapping ends joined together by their interlocking means as each strip is laid down to provide low reluctance lapped joints. The core as thus built up is reformed by the application of pressure into the shape required to fit about a coil winding leg and then annealed to set this shape. The laminations' of strip are then disassembled one at a time and reassembled in the same order about the coil winding leg. My invention may be better understood through a consideration of the following detailed description taken in conjunction with the attached drawings in which:

Figure l is a perspective view of a core formed on a circular arbor showing the lap joints between successive laminations.

Figure 1A shows a lapped joint without detail of the interlocking means.

Figure 2 is a perspective view of a wound core in its deformed shape without detail of lapped joints.

Figure 3 shows an assembled transformer which employs two wound strip cores constructed according to my invention.

Figures 4 and 5 are plan and side elevation views respectively of pre-cut magnetic strip material showing the details of the interlocking means according to the invention.

Figures 6 and 7 illustrate in plan and side elevation respectively two successive layers of magnetic strip con# structed to embody the feature also shown in Figures 4 and 5.

In greater detail, the method of constructing and practising my invention is as follows: t

Strips of magnetic material are cut to a single uniform predetermined Size, and an initial strip 2 is tightly wound flatwise about a circular arbor 1 as shown in Figure 1. The length of the magnetic strip material is not critical, but it has been discovered that a length equal to about two circumferences of the circular arbor gives good results. A second strip 3 is then lapped over the end of strip 2 a distance sufiicient to give a good ux path, interlocked thereto and this strip is then wound tightly around strip 2. The amount of overlap required to give the proper flux path will vary with the material used and the contemplated use of the core, but generally it has been found that an overlap of approximately a half inch gives good results. Similarly, the beginning of each successive strip is lapped over the preceding strip, and thus a core as shown in Figure 1 is built up by successive laminations of strip material. It will be noted that since the strips are of uniform length, the lap joints between successive laminations of strip will be distributed in a fairly even manner around the core, thus giving a reasonably uniform cross section around its whole circumference. Also, since the strips are -wound about ka `rcircular arbor, it is possible to obtain a much tighter and more uniform engagement between successive strips than would be the case if the strips were wound about a non-circular arbor.

It will be necessary at this stage to restrain the circular core in some manner to ensure its retaining the shape shown in Figure 1. This may be accomplished by banding the core or by any other convenient manner.

The core thus built up is then deformed, by the application of heat and pressure, into the shape required to t the winding leg of the coil. A common shape required is shown in Figure 2,v but it is to be understood Vthat the core built up as already described, and illustrated inFigure 1, may be shaped into any other shape to suit varying or specialized applications.

Having been shaped as shown in Figure 2 or as otherwise desired, the core is then annealed'in order to remove deleterious strains and to give the material a permanent set to the desired shape. After'annealing, the core may be removed of -all restraint, and it will remain in its deformed position.

In order to assemble the-thus prepared core around the leg lof a preformed conductive winding structure, the laminations of strip making up the core `are separated from the thus formed core and, beginning with the inside lamination, are then reassembled in the same order about the winding leg. The ends of each lamination may be easily separated a distance suicient to place it around the winding leg, and the core shown in Figure 2 reassembled about the winding leg.

Figure 3 shows the usual arrangement of a transformer c'oil l4 with two cores formed and assembled'according to my invention.

After the core has been so assembled in its'fnal position, it may be banded as with a metal band 5 to hold the whole assembly firmly and positivelyV together.

The core thus produced has been found, in practice, to have excellent magnetic properties, and owing to the fact that one sizeof strip only is required, such a core may be easily and cheaply produced.

The magnetic properties of the core are enhanced by the interlocking means between successive overlapping strips.

Such` means may be that as shown in Figures 4 to 7.

According to this feature, the pre-cut stripsof magnetic material are punched or otherwise provided with anarrow slit 7 close to one end of the strip, and a punched portion as shown at 8 having three sides punched. Portion 8 may then be pushed outwardly from the surface of strip 6 about the non-punched side, as shown best .n Figure 5.

As above described, the first strip (for example, 6) starting with the. end having the slit 7, is wound about the circular arbor. After being lso wound, the punched portion 8 may be withdrawn from the surface of the strip to assume a position as shown in Figure 5.

The Ynext strip 6A isthen placed over this first strip, and the punched portion 8 of the lirst strip is inserted into slit 7A of the second strip, locking the two strips firmly together,` whereupon strip 6A is wound tightly about strip 6.

It will be appreciated that the width of -slit 7 must be at least slightly greater than the thickness of one of the strips, and that its length must be atleast greater than the -length of the non-punched sideof portion 8. In addition, the ,distance between slit 7 and 8 from the edge of the strip `will determine the amount by which succeeding layers overlap. `It will also be appreciated that to obtain a firm lock between successive strips, the side of punched portion 8 which is not punched, kmust be that closest toi the end of strip 6 in order to have this punched portiontassumefthe position shown-in Figure 5 when withdrawn from the surfacefof strips and thus provide azsecure lockowiththe slit. 7A1of. the successive layer, It

4 should be noted that the strips of magnetic material are still of uniform size and dimensions when this embodiment of my invention is applied, and that a single die may be used to form all strips.

It will be appreciated that the precise locking arrangement shown is exemplary only. Many forms of locking means will be readily apparent, and such as corne within the scope and purview of the appended claims are to be considered as part of my invention.

As shown in Figures 6 and 7, the outer end of the punchedv portion 8 is bent inwardly against the top of the end of the strip `6A so that the overlapping ends of the adjoining strips are positively retained in tight face-toface contact substantially over the entire overlapped area to positively prevent separation of the overlapped ends radially of the-core. Thus, goodtcontact between each adjoining pair of overlapping strips is obtained to impart excellent magnetic properties to the core.

While I have described abovein detail the methodof construction of a wound strip core, it is to be understood that my invention is not to be limited to the constructional details disclosed therein, and such embodiments as come within the scope and purview of the appended claims are to be considered as part of my invention.

This is a continuation-in-part of my co-pending application Serial No. 424,450, filed April 20, 1954, entitled Lock Wound Cores.

What I claim -as my invention is:

l. A laminated magnetic core comprising a plurality of strips of magnetic material Wound successively upon one another, there being a plurality of joints between adjoining strips with succeeding joints being spacedapart circumferentially of said core, at each. of said joints the inner end of the successive strip directly overlapping the outer end of its preceding strip a distance suicientto provide a good ilux path therebetween, the overlapping ends of adjoining strips being provided at each'of said joints withy separate interlocking means, each'of said interlocking means comprising a pair ofseparably interlocked elements attached to adjoining ones of said overlapping ends to positively retain said overlapping ends in tight face-to-fa'ce contact substantially over the entire overlapped area and to positively prevent separation of said overlapping ends radially of the core.

2. A laminated magnetic core as recited in` claim 1 wherein said interlocking'means comprises corresponding slot and tongue means, each strip being provided with a slot at one end and a tongue at the other end, said tongue being adaptedfor insertion in -the slot of an adjacent strip to engage said adjacent strip to form said interlocking means.

. 3. A laminated magnetic core as recitedin claim 2 wherein the tongue in each of said strips comprises an integral portion of the strip severed therefrom and bent outwardly from the surface of the-strip about aside attached to thetstrip.

4. A laminated magnetic core as recited in claimA 3 whereinsaid attached side is adjacent the endof the strip.

5. A laminated magnetic core comprising a plurality of strips of magnetic material of substantially uniform length .woundsuccessively upon one another, there being a plurality of joints between adjoining strips with succeeding joints being spaced apart 'circumferentially of said core, at each of said jointsv the inner end of the successive strip directly overlapping the outer end of its preceding strip a distance sufficient to provide a good flux path therebetween, the overlapping ends of adjoining strips being provided ateach of said joints with separate interlocking means, eachof said interlocking meanscornprisingfa pair of separably interlocked elements attached to adjoiningones of said overlapping ends to positively retain saidoverlapping ends in tight` face-to-face contact substantially over the entire overlapped area and to positively prevent separation of said overlapping ends radially oi the core.

6. A laminated magnetic core as recited in claim 5 wherein said interlocking means comprises corresponding slot and tongue means, each strip being provided with a slot at one end and a tongue at the other end, said tongue being adapted for insertion in the slot of an adjacent strip to engage said adjacent strip to form said interlocking means.

7. A laminated magnetic core as recited in claim 6 wherein the tongue in each of said strips comprises an integral portion of the strip severed therefrom and bent outwardly from the surface of the strip about a side attached to the strip.

8. A laminated magnetic core as recited in claim 7 wherein said attached side is adjacent the end of the strip.

References Cited in the le of this patent UNITED STATES PATENTS Vienneau Dec. 22, 1942 Zimsky Feb. 27, 1951 FOREIGN PATENTS Great Britain May 13, 1940 

